Low modulus covered golf balls

ABSTRACT

The present invention is directed to improved cover compositions for golf ball construction and the resulting low modulus golf balls produced utilizing the improved cover compositions. The novel golf ball cover compositions of the invention comprise a blend of a relatively low amount of at least one hard ionomeric resins and a relatively large amount (i.e. from about 75 to about 85-90 percent) of at least one soft ionomer resin. When the cover compositions of the invention are utilized to manufacture golf balls, the golf balls produced thereby, exhibit properties of improved playability at low swing speeds without substantial sacrifices in durability and/or distance characteristics when compared to known hard-soft ionomer blends.

This application is a continuation-in-part of U.S. application Ser. No. 08/645,185, filed May 13, 1996, which is a continuation of U.S. application Ser. No. 08/218,699, filed Mar. 28, 1994 (abandoned), which is a continuation of U.S. application Ser. No. 07/860,455, filed Mar. 30, 1992 (abandoned), which is a continuation-in-part of U.S. application Ser. No. 07/559,177, filed Jul. 27, 1990 (U.S. Pat. No. 5,120,791); and, this application is also a continuation-in-part of U.S. application Ser. No. 08/647,276, filed May 13, 1996 (abandoned), which is a continuation of U.S. application Ser. No. 08/376,281, filed Jan. 20, 1995 (abandoned) which is a continuation of U.S. application Ser. No. 07/927,922, filed Aug. 6, 1992 (abandoned), which is a continuation-in-part of U.S. application Ser. No. 07/865,212, filed Apr. 8, 1992 (U.S. Pat. No. 5,324,783), which is a continuation-in-part of U.S. application Ser. No. 07/559,177, filed Jul. 27, 1990 (U.S. Pat. No. 5,120,791).

BACKGROUND OF THE INVENTION

The present invention concerns improved hard-soft ionomeric resin mixtures (or blends) which are particularly well suited for the formulation of the cover composition of a golf ball. In addition, the present invention is directed to the improved low modulus golf balls produced utilizing the cover compositions of the invention.

More specifically, the present invention relates to novel golf ball cover compositions of low modulus blends comprising about 25 to about 10 (preferably from less than 25 to about 15) weight percent of hard ionomer resins and from about 75 to about 90 (preferably from greater than 75 to about 85) weight percent of soft ionomer resins. The new compositions of the present invention, when utilized for golf ball construction, particularly the construction of two piece golf balls, produce golf balls exhibiting enhanced playability (spin rate) characteristics without substantially sacrificing such properties as travel distance, roundness, impact resistance and/or durability.

Ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability, and flight characteristics, various ionomeric resins sold by E.I. DuPont deNemours & Company (see U.S. Pat. No. 4,884,814) under the trademark “Surlyn® and more recently, by the Exxon Corporation (see U.S. Pat. No. 4,911,451) under the trademarks “Escor®” and the tradename “Iotek”, have become the materials of choice for the construction of golf ball covers over the traditional “balata” (trans polyisoprene, natural or synthetic) rubbers. The softer balata covers, although exhibiting enhanced playability properties, lack the durability necessary for repetitive play.

Ionomeric resins are generally ionic copolymers of an olefin such as ethylene and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacrylic acid, or maleic acid. Metal ions, such as sodium or zinc, are used to neutralize some portion of the acidic groups in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e. improved durability, etc., for golf ball cover construction over balata. However, the advantages gained in increased durability have been offset to some degree by the decreases produced in playability. This is because although the ionomeric resins are very durable, they tend to be very hard when utilized for golf ball cover construction, and thus lack the degree of softness required to impart the spin necessary to control the ball in flight.

As a result, while there are currently more than fifty commercial grades of ionomers available from DuPont and Exxon with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (i.e. relative content of ethylene and methacrylic and/or acrylic acid groups) and additive ingredients such as reinforcements, etc., a great deal of research continues in order to develop golf ball cover compositions exhibiting not only the improved impact resistance and carrying distance properties produced by the “hard” ionomeric resins, but also the playability (i.e. “spin”) characteristics previously associated with the “soft” balata covers, properties which are still desired by the more skilled golfer.

In various attempts to produce such an ideal golf ball, the golfing industry has blended the hard ionomeric resins with a number of softer polymeric materials, such as softer polyurethanes. However, the blends of the hard ionomer resins with the softer polymeric materials have generally been dissatisfactory in that these balls exhibit numerous processing problems. In addition, the balls produced by such a combination are usually short on distance.

In addition, various “hard-soft ionomeric blends”, i.e. mixtures of ionomer resins which are significantly different in hardness and/or flexural modulus, have been attempted. However, until the development of the specific blend combination set forth in U.S. Pat. No. 4,884,814, directed to relatively low modulus golf ball cover compositions, these balls were not particularly commercially viable. In this regard, although the balls produced using the hard-soft ionomer blends exhibited enhanced playability characteristics, they lacked the durability needed for continuous play.

U.S. Pat. No. 4,884,814, one of the inventor's previous patents, is directed to the finding that if various “hard” methacrylic acid based ionomer resins (i.e. those ionomer resins having a hardness of about 60 to 66 on the Shore D scale as measured in accordance with ASTM method D-2240) were blended with similar or larger quantities of one or more “soft” ionomer methacrylic acid based ionomer resins (i.e. those ionomer resins having a hardness from about 25 to 40 as measured on the Shore D scale) that relatively low modulus golf ball cover compositions could be produced that are not only softer than the prior art hard ionomer covers but also exhibit a sufficient degree of durability for repetitive play. These relatively low modulus cover compositions were generally comprised of from about 25 to about 70 weight percent of hard ionomer resins and from about 30 to about 75 weight percent of soft ionomer resins. The incorporation of larger percentages of soft ionomer resin into the cover formulations was generally deemed to be undesirable due to the sacrifices in distance and/or durability that were produced thereby.

However, notwithstanding the above, it has now been found that specific hard/soft ionomer resin blends comprising from about 25 to about 10 (preferably from less than 25 to about 15) weight percent of one or more hard ionomer resins and from about 75 to about 90 (preferably from greater than 75 to about 85) weight percent of one or more soft ionomer resins offer, when utilized for golf ball cover construction, particular advantages to the high skilled professional golfer. Specifically, it has been found that golf balls produced using the new low modulus cover compositions of the invention exhibit high spin rates at very low club head speeds. These balls offer particular utility for the highly skilled and/or professional golfer who desires greater control on the low club head speed “pitch” or “wedge” shots.

In the past, covers composed of high levels of soft ionomers were considered to be nonfunctional due to the drop off in C.O.R. (i.e. travel distance) and cut resistance that accompanied the increase in softness. However, for the P.G.A. Touring Professional Golfer and other highly skilled golfers, distance and durability are generally not a concern. Along these lines, the P.G.A. Touring Professional Golfer will almost never mis-hit a ball badly enough to cut the cover. In addition, the club head speed generated by professional golfers is typically much higher than the amateur, thereby producing greater distance. Thus, the resilience characteristic of the ball is of less importance for the professional golfer than for the average player.

Moreover, the P.G.A. Touring Professional Golfer is usually willing to sacrifice distance for added control, particularly with respect to shots around the green. It is in these pitch, or half and quarter wedge shots that the balls of the present invention show a distinct advantage over the hard/soft ionomer blends of the prior art and the balata covered wound balls.

The present invention is directed to new golf ball cover compositions which exhibit properties of enhanced playability characteristics (i.e. softness and spin) over known hard-soft ionomer blends and the balata-covered wound balls. It has been found that these properties can be produced using improved hard-soft ionomer blends of the present invention in order to produce a low modulus golf ball cover.

The foregoing has outlined some of the most pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention, the detailed description of the invention and the claims which follow below.

SUMMARY OF THE INVENTION

The present invention is directed to improved cover compositions for golf ball construction and the resulting golf balls produced utilizing the improved cover compositions. The novel golf ball cover compositions of the invention comprise a blend of hard ionomeric resins, preferably acrylic acid based ionomers, and recently developed acrylic acid based soft ionomers. When the cover compositions of the invention are utilized to manufacture golf balls, the golf balls produced thereby, exhibit properties of improved distance without sacrificing playability and/or durability when compared to known hard-soft ionomer blends.

The novel golf ball cover compositions of the invention comprise a blend of about 25 to about 10 (preferably from less than 25 to about 15) weight percent of hard ionomeric resins and from about 75 to about 90 (preferably from about 10 to greater than 75) of soft ionomer resins. In the more preferred embodiment of the invention, the soft ionomer resins are methacrylic and acrylic acid based soft ionomer resins. Most preferably, the soft ionomer resins are acrylic acid based soft ionomers. When the cover compositions of the invention are utilized to manufacture golf balls, the golf balls produced thereby exhibit properties of improved playability characteristics, particularly at low swing speeds, without producing substantial sacrifices in distance and/or durability when compared to known hard-soft ionomer blends.

Two of the principal properties involved in the performance of golf balls are resilience and hardness. Resilience is determined by the coefficient of restitution (C.O.R.), the constant “e”, which is the ratio of the relative velocity of two elastic spheres after direct impact to that before impact. As a result, the coefficient of restitution (i.e. “e”) can vary from zero to one, with one being equivalent to an elastic collision and zero being equivalent to an inelastic collision.

Resilience (C.O.R.), along with additional factors such as club head speed, angle of trajectory, and ball configuration (i.e. dimple pattern), generally determines the distance a ball will travel when hit. Since club head speed and the angle of trajectory are not factors easily controllable, particularly by golf ball manufacturers, the factors of concern among manufacturers are the coefficient of restitution (C.O.R.) and the surface configuration of the ball.

The coefficient of restitution (C.O.R.) in solid core balls is a function of the composition of the molded core and of the cover. In balls containing a wound core (i.e. balls comprising a liquid or solid center, elastic windings, and a cover), the coefficient of restitution is a function of not only the composition of the center and cover, but also the composition and tension of the elastomeric windings. Although both the core and the cover contribute to the coefficient of restitution, the present invention is directed solely to the coefficient of restitution which is affected by the cover composition.

In this regard, the coefficient of restitution of a golf ball is generally measured by propelling a ball at a given speed against a hard surface and measuring the ball's incoming and outgoing velocity electronically. As mentioned above, the coefficient of restitution is the ratio of the outgoing velocity to incoming velocity. The coefficient of restitution must be carefully controlled in all commercial golf balls in order for the ball to be within the specifications regulated by the United States Golf Association (U.S.G.A.). Along this line, the U.S.G.A. standards indicate that a “regulation” ball cannot have an initial velocity (i.e. the speed off the club) exceeding 255 feet per second. Since the coefficient of restitution of a ball is related to the ball's initial velocity, it is highly desirable to produce a ball having a sufficiently high coefficient of restitution to closely approach the U.S.G.A. limit on initial velocity, while having an ample degree of softness (i.e. hardness) to produce enhanced playability (i.e. spin, etc.).

The hardness of the ball is the second principal property involved in the performance of a golf ball. The hardness of the ball can affect the playability of the ball on striking and the sound or “click” produced. Hardness is determined as the deformation (i.e. compression) of the ball under various load conditions applied across the ball's diameter (i.e. the lower the compression value, the harder the material). The “softer” covers permit the accomplished golfer to impart proper spin. This is because the softer covers deform on impact significantly more than balls having “harder” ionomeric resin covers. As a result, this allows the better player to impart fade, draw, or backspin to the ball thereby enhancing playability. Such properties can be determined by various “spin rate tests”, such as the “nine-iron” spin rate test set forth below.

Accordingly, the present invention is generally directed to new hard-soft ionomer blends which produce, upon molding around solid or wound cores to formulate a low modulus cover composition, golf balls exhibiting enhanced playability (i.e. hardness/softness, spin rates, etc.) properties without substantially adversely affecting the ball's durability (i.e. impact resistance, etc.) and distance characteristics when utilized by the more skilled or professional golfer. The golf balls which produce high spin rates even at very low club head speeds have particular utility for the professional golfer who desires greater control or “pitch” or “wedge” shots.

These and other objects and features of the invention will be apparent from the following description and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings which are presented for the purposes of illustrating the invention and not for the purposes of limiting the same.

The FIGURE shows a partially broken-away view of an embodiment of a golf ball according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to improved cover compositions for golf ball construction. More particularly, the present invention is directed to improved blends of hard and soft ionomers, which, when utilized to formulate the cover stock of golf balls, produce low modulus golf balls having enhanced properties, including longer distance with similar or improved playability properties (i.e. higher Riehle compression, lower Shore hardness values, high spin rates at low club head speeds, etc.), when compared to golf balls produced by the hard-soft ionomer blends of the prior art. The improved properties produced by the hard-soft ionomer blends of the present invention are due to the use of recently developed acrylic acid based soft ionomers, which produce cover compositions having lower flexural modulus and hardness (i.e. enhanced softness) and improved coefficients of restitution when incorporated with the hard ionomer resins indicated below.

The improved properties produced by the hard-soft ionomer blends of the present invention are due to the use of high amounts (i.e. from about or above 75 to about 85-90 weight percent) of soft ionomers, which, when incorporated with low amounts (i.e. from about or below 25 to about 15-10 weight percent) of the hard ionomer resins, produce cover compositions having lower flexural modulus and hardness (i.e. enhanced softness). The cover compositions when molded around wound or solid cores, produce two-piece or multi-layered golf balls having enhanced playability (spin rates) characterization versus the prior art and balata-covered wound balls at any club head speed, and particularly at very low swing speeds.

The hard (high modulus) ionomers suitable for use in the present invention include those ionomers having a hardness greater than 50 on the Shore D scale as measured in accordance with ASTM method D-2240, and a flexural modulus from about 15,000 to about 70,000 psi as measured in accordance with ASTM method D-790.

The hard ionomer resins utilized to produce the cover compositions are ionic copolymers which are the sodium, zinc, magnesium or lithium salts of the reaction product of an olefin having from 2 to 8 carbon atoms and an unsaturated monocarboxylic acid having from 3 to 8 carbon atoms. The carboxylic acid groups of the copolymer may be totally or partially (i.e. approximately 15-75 percent) neutralized.

Preferably, the hard ionomeric resins are copolymers of ethylene and either acrylic and/or methacrylic acid, with copolymers of ethylene and methacrylic acid being the most preferred. In addition, two or more types of hard ionomeric resins may be blended into the cover compositions in order to produce the desired properties of the resulting golf balls.

Although the scope of the patent embraces all known hard ionomeric resins falling within the parameters set forth above, only a relatively limited number of these hard ionomeric resins are commercially available. In this regard, the hard ionomeric resins sold by E.I. DuPont de Nemours Company under the trademark “Surlyn®”, and the hard ionomer resins sold by Exxon Corporation under either the trademark “Escor®” or the tradename “Iotek” are examples of commercially available hard ionomeric resins which may be utilized in the present invention in the particular combinations described in detail below.

The hard ionomeric resins introduced under the designation “Escor®” and now sold under the new designation “Iotek”, are somewhat similar to the hard ionomeric resins sold under the “Surlyn®” trademark. However, since the “Iotek” ionomeric resins are sodium or zinc salts of poly(ethylene acrylic acid) and the “Surlyn” resins are zinc, sodium or lithium salts of poly(ethylene methacrylic acid) some distinct differences in properties exist. In addition, various blends of “lotek” and “Surlyn” hard ionomeric resins, as well as other available ionomeric resins, may be utilized in the present invention.

Examples of commercially available hard ionomeric resins which may be utilized in the present invention include, but are not limited to, the hard sodium ionic copolymer sold under the trademark “Surlyn® 8940”, the hard zinc ionic copolymer sold under the trademark “Surlyn 9910®” and the hard lithium ionic copolymers sold under the trademark “Surlyn® 7930” or “Surlyn® 7940”. Surlyn 8940 is a copolymer of ethylene with methacrylic acid with about 15 weight percent acid which is about 29% neutralized with sodium ions. This resin has an average melt flow index of about 2.8. Surlyn 9910 is a copolymer of ethylene and methacrylic acid with about 15 weight percent acid which is about 58% neutralized with zinc ions. The average melt flow index of Surlyn 9910 is about 0.7. Surlyn® 7930 and Surlyn® 7940 are two similar lithium neutralized poly(ethylene-methacrylic acid) ionomers differing in melt indexes. The typical properties of Surlyn 9910 and 8940 are set forth below in Table 1.

TABLE 1 Typical Properties of Commercially Available Hard Surlyn ® Resins Suitable for Use in the Present Invention ASTM D 8940 9910 8920 8528 9970 9730 7940 Cation Type Sodium Zinc Sodium Sodium Zinc Zinc Lithium Melt flow index, D-1238 2.8 0.7 0.9 1.3 14.0 1.6 3.0 gms/10 min. Specific Gravity, D-792 0.95 0.97 0.95 0.94 0.95 0.95 0.93 g/cm³ Hardness, Shore D D-2240 66 64 66 60 62 63 64 Tensile Strength, D-638 (4.8) (3.6) (5.4) (4.2) (3.2) (4.1) (3.7) (kpsi), MPa 33.1 24.8 37.2 29.0 22.0 28.0 Elongation, % D-638 470 290 350 450 460 460 220 Flexural Modulus, D-790  (51)  (48)  (55)  (32)  (28)  (30)  (61) (kpsi) MPa Tensile Impact (23° C.) D-18225 1020  1020  865 1160  760 1240  KJ/m₂ (ft.-lbs./in²) (485) (485) (410) (550) (360) (590) Vicat Temperature, ° C. D-1525  63  62  58  73  61  73

In addition, examples of the acrylic acid based hard ionomer resins suitable for use in the present invention sold under the “Iotek” tradename by the Exxon Corporation include “Iotek 4000” (formerly “Escor 4000”), “Iotek 4010”, “Iotek 8000” (formerly Escor 900), “Iotek 8020”, and “Iotek 8030”. The typical properties of the Iotek hard ionomers are set forth below in Table 2.

TABLE 2 Typical Properties of Iotek Ionomers ASTM Method Units 4000 4010 8000 8020 8030 Resin Properties Cation type zinc zinc sodium sodium sodium Melt index D-1238 g/10 min. 2.5 1.5 0.8 1.6 2.8 Density D-1505 kg/m³ 963 963 954 960 960 Melting Point D-3417 ° C. 90 90 90 87.5 87.5 Crystallization Point D-3417 ° C. 62 64 56 53 55 Vicat Softening Point D-1525 ° C. 62 63 61 64 67 % Weight Acrylic Acid 16 11 % of Acid Groups 30 40 cation neutralized Plaque Properties (3 mm thick, compression molded) Tensile at break D-638 MPa 24 26 36 31.5 28 Yield point D-638 MPa none none 21 21 23 Elongation at break D-638 % 395 420 350 410 395 1% Secant modulus D-638 MPa 160 160 300 350 390 Shore Hardness D D-224D — 55 55 61 58 59 Film Properties (50 micron film 2.2:1 Blow-up ratio) Tensile at Break MD D-882 MPa 41 39 42 52 47.4 TD D-882 MPa 37 38 38 38 40.5 Yield point MD D-882 MPa 15 17 17 23 21.6 TD D-882 MPa 14 15 15 21 20.7 Elongation at Break MD D-882 % 310 270 260 295 305 TD D-882 % 360 340 280 340 345 1% Secant modulus MD D-882 MPa 210 215 390 380 380 TD D-882 MPa 200 225 380 350 345 Dart Drop Impact D-1709 g/micron 12.4 12.5 20.3

The soft (low modulus) ionomers utilized to formulate the blends of the present invention are acrylic acid or methacrylic acid based soft ionomers. These soft ionomers may be generally characterized as comprised of sodium, zinc, magnesium or lithium salts of the reaction product of an olefin having from about 2 to 8 carbon atoms, acrylic or methacrylic acid, and an unsaturated monomer of an acrylated ester class having from 1 to 21 carbon atoms. The carboxylic acid groups of the copolymer may be totally or partially (i.e. about 15-75 percent) neutralized).

Preferably, the soft ionomer resins are sodium or zinc salt of a terpolymer of an olefin having 2 to 8 carbon atoms, either acrylic and/or methacrylic acid, and an unsaturated monomer of an acrylated ester class having from 1 to 21 carbon atoms, with those comprising ethylene, methacrylic acid and methyl or butyl acrylate being the more preferred. Moreover, two or more types of soft ionomer resins may be blended into the cover compositions in order to produce the desired properties of the resulting golf balls.

Most preferably, the soft (low modulus) ionomers utilized to formulate the blends of the present invention are acrylic acid based soft ionomers. These soft ionomers may be generally characterized as comprised of sodium or zinc salts of a terpolymer of an olefin having from about 2 to 8 carbon atoms, acrylic acid, and an unsaturated monomer of the acrylate ester class having from 2 to 22 carbon atoms. Preferably, the soft ionomer is a zinc based ionomer made from an acrylic acid base polymer and an unsaturated monomer of the acrylate ester class. The soft (low modulus) ionomers have a hardness from about 20 to about 40 (preferably from about 30 to about 40) as measured on the Shore D scale and a flexural modulus from about 2,000 to about 10,000 psi (preferably from about 3,000 to 7,000 psi) as measured in accordance with ASTM method D-790.

More particularly, the present inventors have discovered that if relatively high amounts of the above indicated soft ionomers are utilized with the specific hard ionomers described above, in the combinations more clearly defined below and demonstrated in the Examples, the overall combinations, when utilized for golf ball construction, produce golf balls having higher spin rates at low swing speeds (i.e. full nine iron, full wedge and open wedge shots), lower hardness values and relatively similar C.O.R. and compression values than golf balls produced by various hard-soft ionomer blends, including the hard-soft ionomer blends utilized to produce Spalding's current Tour Edition® 100 ball (i.e. U.S. Pat. No. 4,884,814). Moreover, when compared to commercially available balata-covered golf balls such as the Titleist® Tour 100 available from Acushnet Co., the golf balls of the present invention exhibit improved spin rates, C.O.R. (i.e. distance) and durability values.

In addition, the present inventors have discovered that if the new acrylic acid based experimental soft ionomers recently developed by the Exxon Corporation for the Spalding Sports Worldwide, a division of Spalding & Evenflo Companies, Inc., Tampa, Fla., are utilized with the specific hard ionomers described above, in the combinations more clearly defined below and demonstrated in the Examples, not only are improvements in processability and clarity seen, but also the overall combinations, when utilized for golf ball construction, produce golf balls having higher coefficient of restitution values (i.e. longer distance) at equal or softer hardness than golf balls produced by known hard-soft ionomer blends, including the hard-soft ionomer blends utilized to produce Spalding's current Tour Edition® ball.

Examples of the soft ionomer resins suitable for use in the invention include the ethylene-acrylic acid based soft ionomer resins recently developed by the Exxon Corporation under the designations “Iotek 7520” (referred experimentally by differences in neutralization and melt indexes as LDX 195, LDX 196, LDX 218 and LDX 219) and “Iotek 7510” and the ethylene-methacrylic acid based soft-ionomers sold by DuPont under the designations “Surlyn® 8265” and “Surlyn® 8269”.

In this regard, the inventors have found that when the new ethylene-acrylic acid based soft ionomer resins recently developed by the Exxon Corporation under the designations “Iotek 7520” and “Iotek 7510” are combined with the known hard ionomers indicated above, the combination produces higher C.O.R.s at equal or softer hardness, higher melt flow (which corresponds to improved, more efficient molding, i.e. fewer rejects), as well as significant cost savings versus balls produced by known hard-soft ionomer blends due to lower overall raw materials cost and improved yields.

While the exact chemical composition of the resins to be sold by Exxon under the designation Iotek 7520 is considered by Exxon to be confidential and proprietary information, Exxon's Experimental Product Data sheet lists the following physical properties of the ethylene acrylic acid zinc ionomer developed by Exxon:

TABLE 3 Property ASTM Method Units Typical Value Physical Properties of Iotek 7520 Melt Index D-1238 g/10 min. 2 Density D-1505 kg/m³ 0.962 Cation Zinc Melting Point D-3417 ° C. 66 Crystallization D-3417 ° C. 49 Point Vicat Softening D-1525 ° C. 42 Point Plaque Properties (2 mm thick Compression Molded Plaques) Tensile at Break D-638 MPa 10 Yield Point D-638 MPa None Elongation at Break D-638 % 760 1% Secant Modulus D-638 MPa 22 Shore D Hardness D-2240 % 32 Flexural Modulus D-790 MPa 26 Zwick Rebound ISO 4862 % 52 De Mattia Flex D-430 Cycles >5000 Resistance

In addition, test data collected by the inventors indicates that Iotek 7520 resins have Shore D hardnesses of about 32-36 (per ASTM D-2240), melt flow indexes of 3±0.5 g/10 min (at 190° C. per ASTM D-1288), a flexural modului of about 2500-3500 psi (per ASTM D-790). Furthermore, testing by an independent testing laboratory by pyrolysis mass spectrometry indicates that the Iotek 7520 and Iotek 7510 resins are generally zinc salts of a terpolymer of ethylene, acrylic acid, and methyl acrylate.

Examples of the methacrylic acid based soft (low modulus) ionomer resins suitable for use in the invention include Surlyn® 8265 and Surlyn® 8269. The typical properties of these ionomers are listed below:

TABLE 4 Typical Properties of Surlyn ® Low Modulus Ionomer Resins Typical Properties ASTM-D AD-8265 AD-8269 Cation Type Sodium Sodium Melt Flow Index, gms/10 min. D-1238 0.9 0.9 Specific Gravity D-792 0.94 0.94 Hardness, Shore A/D 92/39 84/25 Tensile Strength, (kpsi) MPa D-638 (4.2) 28.8 (3.1) 21.2 Elongation, % D-638 660 770 Flexural Modulus, (kpsi) MPa D-790 (7.1) 49.1 (2.8) 19.3 Tensile Impact (23° C.) KJ/m² D-18225 494 (235) 447 (213) (ft-lbs/in²) Melting Point, ° C. DTA 81 72 Freezing Point, ° C. DTA 51 38 Vicat Temperature, ° C. D-1525 51 48

Furthermore, the inventors have found that the acrylic acid based soft ionomer available from the Exxon Corporation under the designation Iotek 7510, is also effective, when combined with the hard ionomers indicated above in producing golf ball covers exhibiting higher C.O.R. values at equal or softer hardness than those produced by known hard-soft ionomer blends. In this regard, Iotek 7510 produces golf balls which have the advantages (i.e. improved flow, higher C.O.R. valves at equal hardness, increased clarity, etc.) produced by the Iotek 7520 resin when compared to the methacrylic acid base soft ionomers blends known in the art (such as the Surlyn 8265 and the Surlyn 8269 combinations disclosed in U.S. Pat. No. 4,884,814).

In addition, Iotek 7510, when compared to Iotek 7520, produces slightly higher C.O.R. valves at equal softness/hardness due to the Iotek 7510's higher hardness and neutralization. Similarly, Iotek 7510 produces better release properties (from the mold cavities) due to its slightly higher stiffness and lower flow rate than Iotek 7520. This is important in production where the soft covered balls tend to have lower yields caused by sticking in the molds and subsequent punched pin marks from the knockouts.

According to Exxon, Iotek 7510 is of similar chemical composition as Iotek 7520 (i.e. a zinc salt of a terpoloymer of ethylene, acrylic acid, and methyl acrylate) but is more highly neutralized. Based upon FTIR analysis, Iotek 7520 is estimated to be about 30-40 wt. % neutralized and Iotek 7510 is estimated to be about 40-60 wt. % neutralized. The typical properties of Iotek 7510 in comparison of those of Iotek 7520 are set forth below:

TABLE 5 Physical Properties of Iotek 7510 in Comparison to Iotek 7520 IOTEK 7520 IOTEK 7510 MI, g/10 min 2.0 0.8 Density, g/cc 0.96 0.97 Melting Point, ° F. 151 149 Vicat Softening Point, ° F. 108 109 Flex Modulus, psi 3800 5300 Tensile Strength, psi 1450 1750 Elongation, % 760 690 Hardness, Shore D 32 35

As mentioned above and more clearly indicated below in the Examples, the recently developed ethylene-acrylic acid based soft ionomers (i.e. the Iotek 7520 and the Iotek 7510 resins) produce, when combined with various hard ionomers, particularly the Escor® hard ionomers, golf balls exhibiting enhanced properties, including longer distance at similar or softer hardness, over known hard-soft ionomer blends including those set forth in the U.S. Pat. No. 4,884,814 concerning related subject matter. Along this line, while the '814 patent is directed to various hard-soft Surlyn® ionomer blends which are similar to those blends utilized to formulate Spalding's current Tour Edition® golf ball, the soft Surlyn ionomers (i.e. the Surlyn 8265 and 8269 resins) disclosed therein are of the poly(ethylene-methacrylic acid-butyl acrylate) type. The inventors have now discovered that the use of soft ionomers containing acrylic acid (i.e. the Iotek 7520 and the Iotek 7510 resins), produce a more desirable golf ball in terms of distance and hardness (softness) while maintaining durability, when used in combination with various known hard resins.

As shown in the FIGURE, the superior golf balls 10 of the present invention containing the improved hard-soft ionomer blends can be generally produced from a central core 12 and an outer cover 14 wherein the outer cover is made from a composition comprised of a blend of from about 25 to about 10 weight percent of at least one hard ionomer resin, and from about 75 to about 90 weight percent of at least one soft ionomer resin. The central core may be solid or wound and additionally may incorporate one or more layers (i.e. multi-layer technology). Preferably, the ionomer resins are methacrylic and acrylic acid based ionomers. Most preferably, acrylic acid based ionomers are used.

More preferably, it has been found that a golf ball exhibiting properties of improved playability (i.e. enhanced spin rates at low club head swing speeds, hardness/softness, compression characteristics etc.) without substantial sacrifices in durability and travel distance, can be produced from a core and a cover, wherein the cover is made from a composition comprised from less than 25 to about 15 weight percent of at least one hard ionomer resin, and from greater than 75 to about 85 weight percent of a soft ionomer, preferably acrylic acid based ionomer resins.

Superior results may be achieved when the hard ionomers utilized are sodium or zinc salts of poly(ethylene acrylic acid) such as those sold by Exxon under the Iotek designation, particularly Iotek 4000 and Iotek 8000, and the soft ionomers utilized are the new acrylic acid based soft ionomers recently developed by Exxon under the designations Iotek 7520 and Iotek 7510.

Additional materials may also be added to the compositions of the present invention, including dyes (for example, Ultramarine Blue sold by Whitaker, Clark, and Daniels of South Plainsfield, N.J.) (see U.S. Pat. No. 4,679,795), pigments such as titanium dioxide, zinc oxide, barium sulfate and zinc sulfate; UV absorbers; antioxidants; antistatic agents; and stabilizers. Generally, the additives are admixed with an ionomer to be used in the cover composition to provide a master batch of desired concentration and an amount of the master batch sufficient to provide the desired amounts of additives is then admixed with the ionomer blends. Moreover, the cover compositions of the present invention may also contain softening agents, such as plasticizers, processing aids, etc., and reinforcing materials such as glass fibers and inorganic fillers, as long as the desired properties produced by the golf ball covers of the invention are not impaired.

The cover compositions of the present invention may be produced according to conventional melt blending procedures. Generally, the hard ionomer resins are blended with the soft ionomeric resins in a Banbury type mixer, two-roll mill, or extruder prior to molding. The blended composition is then formed into slabs and maintained in such a state until molding is desired. If necessary, further additives such as inorganic fillers, antioxidants, stabilizers, and/or zinc oxide may be added and uniformly mixed before initiation of the molding process. Alternatively, a simple dry blend of the pelletized resins and color master batch may be prepared and fed directly into the injection molding machine where homogenization occurs in the mixing section of the barrel prior to injection into the mold.

The golf balls of the present invention can be produced by molding processes currently well known in the golf ball art. Specifically, the golf balls can be produced by injection molding or compression molding the novel cover compositions about wound or solid molded cores to produce a golf ball having a diameter of about 1.680 inches and weighing about 1.620 ounces. The standards 19 for both the diameter and weight of the balls are established by the United States Golf Association (U.S.G.A.). Although both solid core and wound cores can be utilized in the present invention, as a result their lower cost and superior performance, solid molded cores are preferred over wound cores.

Conventional solid cores are typically compression molded from a slug of uncured or lightly cured elastomer composition comprising a high cis content polybutadiene and a metal salt of an α, β, ethylenically unsaturated carboxylic acid such as zinc mono or diacrylate or methacrylate. To achieve higher coefficients of restitution in the core, the manufacturer may include a small amount of a metal oxide such as zinc oxide. In addition, larger amounts of metal oxide than are needed to achieve the desired coefficient may be included in order to increase the core weight so that the finished ball more closely approaches the U.S.G.A. upper weight limit of 1.620 ounces. Other materials may be used in the core composition including compatible rubbers or ionomers, and low molecular weight fatty acids such as stearic acid. Free radical initiator catalysts such as peroxides are admixed with the core composition so that on the application of heat and pressure, a complex curing or cross-linking reaction takes place.

The term “solid cores” as used herein refers not only to one piece cores but also to those cores having a separate solid layer beneath the cover and above the core as in U.S. Pat. No. 4,431,193, and other multi-layer and/or non-wound cores.

Wound cores are generally produced by winding a very long elastic thread around a solid or liquid filled balloon center. The elastic thread is wound around the center to produce a finished core of about 1.4 to 1.6 inches in diameter, generally. Since the core material is not an integral part of the present invention, a detailed discussion concerning the specific types of core materials which may be utilized with the cover compositions of the invention are not specifically set forth herein. In this regard, the cover compositions of the invention may be used in conjunction with any standard golf ball core.

As indicated, the golf balls of the present invention may be produced by forming covers consisting of the compositions of the invention around cores by conventional molding processes. For example, in compression molding, the cover composition is formed via injection at about 380° F. to about 450° F. into smooth surfaced hemispherical shells which are then positioned around the core in a dimpled golf ball mold and subjected to compression molding at 200-300° F. for 2-10 minutes, followed by cooling at 50-70° F. for 2-10 minutes, to fuse the shells together to form an unitary ball. In addition, the golf balls may be produced by injection molding, wherein the cover composition is injected directly around the core placed in the center of a golf ball mold for a period of time at a mold temperature of from 50° F. to about 100° F. After molding the golf balls produced may undergo various further processing steps such as buffing, painting, and marking.

The resulting golf balls produced from the novel hard-soft ionomeric resin combinations of the present invention exhibit enhanced playability properties over the art without significant sacrifices in travel, distance and durability. This is due to the use of the specific hard/soft ionomeric resin blend rations described above and, more specifically, set forth in the Examples below.

The present invention is further illustrated by the following examples in which the parts of the specific ingredients are by weight. It is to be understood that the present invention is not limited to the examples, and various changes and modifications may be made in the invention without departing from the spirit and scope thereof.

EXAMPLES

By blending the ingredients set forth in the Table 6 below, a series of solid molded cores were generated. In this regard, the Pink core is representative of a core for a 90 compression golf ball, while the Green and the White cores are representative of 100 compression golf balls.

In addition, a series of cover compositions were produced according to the formulations set forth in Table 7, wherein, cover Formulations B and C are representative cover compositions comprising methacrylic acid based soft ionomers according to the present invention. Formulation A is representative of the cover composition of U.S. Pat. No. 4,884,814, which also contains methacrylic acid, albeit at an amount which is outside the scope of the present invention.

Utilizing the molded cores of Table 6 and the cover compositions of Table 7, a number of two-piece finished golf balls were formulated according to the processing procedure briefly set forth above. The results produced by the finished balls are set forth in Tables 8 and 9 below. In addition, the properties of the molded balls were also compared to several commercially available golf balls having generally good playability characteristics, including balata cover balls.

In the Examples, cover formulations containing the soft ionomer-hard ionomer blends of the present invention (Examples 3-4 and 8-11) were compared with the hard-soft ionomer blends including the hard-soft ionomer blends utilized to produce the current Tour Edition® 100 ball (see Examples 1-2) which is the subject of U.S. Pat. No. 4,884,814. In addition, the properties produced by the cover compositions formulated with the soft ionomer-hard ionomer blends of the present invention (Examples 3-4 and 8-11) were compared to the properties produced by the commercial representatives of the Tour Edition® 90 (Examples 7 and 15), Tour Edition® 100 (Examples 6 and 14) and the Top Flite® II (Example 16) balls currently being sold by Spalding & Evenflo Companies, Inc., Tampa, Fla., as well as a wide variety of competitive golf balls available in the market place, including the Titleist® Tour 90 and 100 (Balata) balls (Examples 5 and 12-13) sold by the Acushet Co. Along this line, the current Tour Edition® ball is unique in that it is a two piece (solid core, molded cover) ball that meets the needs of golfers who demand superior control, historically obtained only with balata covered wound balls. It offers superior playability with a small sacrifice in coefficient of restitution, which relates directly to distance.

The Tour Edition® 100 ball has a slightly softer cover than the Tour Edition® 90 ball and utilizes a unique 422 Hex dimple design. The Tour Edition® 100 ball more closely meets the demands of the pro tour golfer than any other Spalding ball previously produced.

The Top Flite® ball is considered to be a “hard” Surlyn or Iotek ionomeric resin ball. As a result of the ball's hardness, the Top Flite® ball is a difficult ball for golfers to control. Generally, the harder the golf ball, the more difficult it is for a golfer to impart spin to the ball, and hence, control the ball during flight. However, as a result of its outstanding durability and maximum distance, the ball is widely accepted by a large percentage of golfers.

The Titleist® Tour balls are balata covered, wound balls trademarked and sold by the Acushnet Company. As a result of their traditional presence on the P.G.A. Tour and promotional incentives given P.G.A. pros, they are still the balls most frequently utilized by the P.G.A. Touring Professional Golfers despite substantial drawbacks in durability and distance.

The present invention is directed to various blends of hard ionomers and soft ionomers, which, when utilized for golf ball cover construction, produce low modulus golf balls which exceed playability characteristics of the current Tour Edition® 100 ball and the balata covered Titleist® Tour balls.

In this regard, cover formulations set forth below in Tables 6, 7, 8, and 9 were injection molded at 400° F. around the solid type cores set forth in Table 6 having a finished diameter of about 1.542 to 1.572 inches to produce golf balls approximately 1.680 inches in diameter having nominal cover thickness of 0.0690 to 0.0540 inches. The properties of Riehle compression, coefficient of restitution (C.O.R.), Shore Hardness, impact resistance, and spin rate for the cover formulation were determined. The data for each example represents the average data for one dozen balls produced according to the desired manner. The properties were measured according to the following parameters:

Riehle compression is a measurement of the deformation of a golf ball in inches under a fixed static load of 200 pounds. P.G.A. compression is determined by substrating the Riehle compression from 160.

Coefficient of restitution (C.O.R.) was measured by firing the resulting golf ball is an air cannon at a velocity of 125 feet per second against a steel plate which is positioned 12 feet from the muzzle of the cannon. The rebound velocity was then measured. The rebound velocity was divided by the forward velocity to give the coefficient of restitution.

Shore hardness was measured in accordance with ASTM Test 2240.

Cut resistance was measured in accordance with the following procedure: A golf ball is fired at 135 feet per second against the leading edge of a pitching wedge, wherein the leading edge radius is {fraction (1/32)} inch, the loft angle is 51 degrees, the sole radius is 2.5 inches, and the bounce angle is 7 degrees.

The cut resistance of the balls tested herein was evaluated on a scale of 1-5. 1 represents a cut that extends completely through the cover to the core; a 2 represents a cut that does not extend completely through the cover but that does break the surface; a 3 does not break the surface of the cover but does leave a permanent dent; a 4 leaves only a slight crease which is permanent but not as severe as 3; and a 5 represents virtually no visible indentation or damage of any sort.

The spin rate of the golf ball was measured by striking the resulting golf balls with a 9-iron, a full wedge and an open wedge wherein the club-head speed for the 9-iron is about 105 feet (per second (fps), the full wedge at 95 fps, and the open wedge at 60 fps. The spin rate was measured by observing the rotation of the ball in flight using stop action Strobe photography.

Initial velocity is the velocity of a golf ball when struck at a hammer speed of 143.8 feet per second in accordance with a test as prescribed by the U.S.G.A.

TABLE 6 Core Formulations Ingredients Pink Green White Polybutadiene 100. 100. 100. BR-1220¹ Zinc Diacrylate 29. 26. 33. Zinc Oxide 21. 20.5 19.5 Zinc Stearate 20. 20. 20. Ground Flash 10. 9. 10. Green M.B. — 0.04 — Red M.B. 0.05 — — 231 XL² 0.90 0.60 0.90 Papi 94³ 0.50 0.15 0.50 Total 181.45 176.29 183.90 Properties Molded Core Size, inches 1.542 1.542 1.572 Weight, grams 36.7 36.9 38.6 Riehle Compression 72 64 68 C.O.R. ({overscore (e)}) .800 .816 .805 ¹BR-1220 is a polybutadiene manufactured and sold by Shell Chemical Co., Houston, Texas. ²231 XL is a peroxyketal sold by Atochem, lucidol Division, Buffalo, New York. ³Papi 94 is a polymeric diisocyanate available from Dow Chemical Co., Midland, Michigan.

TABLE 7 Cover Formulations Ingredients A B C Surlyn ® 8269 49.1 59.2 55.7 Surlyn ® 8265 21.4 25.8 24.3 Surlyn ® 9910 15.2 4.1 7.9 Surlyn ® 8940 4.7 1.3 2.5 2714 White MB¹ 9.6 9.6 9.6 Total 100.00 100.00 100.00 ¹2714 White MB (Master Batch) is comprised of 75.85% Surlyn ® 8528, 23.77% Unitane 0-110, 0.05% Ultra Blue, 0.22% Unitex O.B. and 0.03% Santonox R.

TABLE 8 Examples 5 6 7 Titleist ® Tour Tour Tour 100 Edition ® Edition ® Ingredients 1 2 3 4 (Balata) 100 90 Core Form. Pink Green Pink Green Cover Form.² A A C C Properties - Finished Balls Weight, grams 45.4 45.3 45.3 45.3 45.2 45.1 45.2 Comp. (Riehle) 65 59 65 60 72 58 58 C.O.R. ({overscore (e)}) .797 .808 .795 .807 .788 .805 .809 Size, inches 1.682 1.683 1.683 1.683 1.681 1.683 1.682 Shore C 83-84 83-84 78-79 79-80 82-83 84-85 85-86 Hardness Cut Resistance¹ 3-4 3-4 3 3 1 3-4 3-4 Spin Rate 9,186 9,362 9,618 9,644 9,351 9,670 9,389 (RPM) Full #9 Iron Spin Rate 9,512 9,668 10,089 10,203 9,969 9,266 9,051 (RPM) Full Wedge Spin Rate 5,223 5,503 5,853 5,705 5,660 5,143 5,054 (RPM) Open Wedge ¹Cut Resistance -- 5 = No visible marking 1 = Clean cut thru ²Cover formulations 1-4 and 6 were molded in a 422-HEX dimple pattern. Ball 7 is a 422 Tri-dimple pattern

TABLE 9 Examples 14 15 16 12 13 Tour Tour Top Titleist ® Titleist ® Edition ® Edition ® Flite ® Ingredients 8 9 10 11 Tour 100 Tour 90 100 90 XLII Core Form. Pink White White White Cover Form.¹ C C C B Properties- Finished Balls Weight, 45.6 45.5 45.5 45.6 45.1 45.3 45.2 45.5 45.3 grams Comp. 70 73 70 71 71 69 58 56 51 (Riehle) C.O.R. (e) .803 .803 .797 .802 .784 .788 .807 .814 .814 Size, 1.683 1.683 1.682 1.684 1.681 1.682 1.684 1.683 1.681 inches Shore C 77-78 77-78 77-78 74-75 82-83 82-83 84-85 85-86 96 Hardness Cut 3 3 3 3 1 1 3-4 3-4 4-5 Resistance Spin Rate 10,781 10,541 10,939 11,227 11,044 10.779 9.922 9,625 5,742 (RPM) Full Wedge Spin Rate 5,687 5,362 5,399 5,778 5,642 5,655 5,066 5,127 2,893 (RPM) Open Wedge ¹Ball types 8, 9, 11, and 14 were molded in a 422-HEX dimple pattern. Ball nos. 10 and 15 were molded in a 422 Tri-dimple pattern; and No 16 was molded in a 410-Octahelix dimple pattern.

Discussion of the Examples

The above Examples indicate that use of relatively large amounts of soft ionomers (i.e. from about or above 75 to about 85-90 weight percent) in combination with relatively low amounts of hard ionomers (i.e. from about or below 25 to about 15-10 weight percent) produces golf balls exhibiting improved compression and playability characteristics at low swing speeds. Specifically, the Examples of Table 8 (wherein Examples 3 and 4 represent the current invention) indicate the ball properties and spin rates at three different club head speeds (i.e. as indicated above, the full 9-iron was tested at a club head speed of about 105 pfs, the full wedge at 95 fps, and the open wedge at 60 fps). It is demonstrated that while the Tour Edition® 100 ball and the cover formulations of Examples 1 and 2 (i.e. the technology of the U.S. Pat. No. 4,884,814) have spin equal to or exceeding the Titleist® Tour “balata” cover wound ball at the relatively high club head speed produced by a full 9-iron, the spin rates produced using the lower club head speeds of a full or opened wedge is less for the balls of the '814 patent versus the Titleist® balata ball. However, the balls of the present invention (i.e. Examples 3 and 4 in Table 8), exceed the spin rates of the Titleist balata covered wound ball under all conditions while having a higher C.O.R. (enhanced travel distance) and substantially better cut resistance than the balata covered Titleist® balls.

The Examples set forth in Table 9 further demonstrate the advantages in spin rates, C.O.R. and cut resistance of the 80 to 85 weight percent soft ionomer blends of the cover compositions of the present invention (i.e. Examples 8-11) with different compression cores over the balata covered Titleist® wound balls.

The data suggests that the range of the present invention is from about 75 to about 85-90 percent of soft ionomer, a more preferred range being from greater than 75 to about 85 percent of soft ionomer, and a most preferred range being about 85 percent of soft ionomer (i.e. Example 11).

As a result, the new hard-soft ionomer blends of the present invention produce golf balls exhibiting properties of enhanced playability (particularly at low sing speeds) without substantial sacrifices in distance and/or durability.

In addition, cover formulations containing the acrylic acid based soft ionomers-hard ionomer blends of the present invention were compared with the hard-soft ionomer blends of the prior art including the hard-soft ionomer blend utilized to produce the current Tour Edition® ball (see Examples 3, 11 and 24) which is the subject of U.S. Pat. No. 4,884,814.

The properties produced by the cover compositions formulated with the acrylic acid based soft ionomer-hard ionomer blends of the present invention were compared to the properties produced by the cover materials representative of the Tour Edition®, Tour Edition® 100 and the Top Flite® II balls currently being sold by Spalding & Evenflo Companies, Inc., Tampa, Fla., as well as a wide variety of competitive golf balls available in the market place. Although the specific formulations utilized to produce the Tour Edition® 100 and Top Flite® balls are proprietary, these formulations were utilized under the same processing conditions as those set forth below in order to produce covered golf balls for comparison purposes.

Along this line, the current Tour Edition® ball is unique in that it is a two piece solid core, molded cover ball that meets the needs of golfers who demand superior control, historically obtained only with balata covered wound balls. It offers superior playability at the sacrifice of coefficient of restitution, which relates directly to distance.

The Tour Edition® 100 ball has a slightly softer cover than the Tour Edition® ball and utilizes a unique twin-dimple design. The Tour Edition® 100 ball more closely meets the demands of the pro tour golfer than any other Spalding ball previously produced.

The Top Flite® ball is considered to be a “hard” Surlyn or Iotek ionomeric resin ball. As a result of the ball's hardness, the Top Flite® ball is a difficult ball for golfers to control. Generally, the harder the golf ball, the more difficult it is for a golfer to impart spin to the ball, and hence, control the ball during flight. However, as a result of its outstanding durability and maximum distance, the ball is widely accepted by a large percentage of golfers.

The following examples of the present invention are directed to various blends of hard ionomers and acrylic acid based soft ionomers, which, when utilized for golf ball cover construction, produce golf balls closely approaching the superior distance properties exhibited by the current Top Flited ball without sacrificing the playability characteristics of the current Tour Edition® ball.

The cover formulations set forth below in Tables 10, 11 and 12 were injection molded at 400° F. around identical solid type cores having a finished diameter of 1.545 inches to produce golf balls approximately 1.680 inches in diameter having nominal cover thickness of 0.0675 inches. The properties of Riehle compression, coefficient of restitution (C.O.R.), Shore Hardness, impact resistance, and spin rate for the cover formulation were determined. In Tables 10 and 11, Examples 3 and 11 are identical, and Examples 19 and 22 are similar in composition (i.e. different neutralization and melt index grades of Iotek 7520 where utilized). These Examples have been set forth for comparison purposes. The data for each example represents the average data for one dozen balls produced according to the desired manner. The properties were measured according to the following parameters:

Riehle compression is a measurement of the deformation of a golf ball in inches under a fixed static load of 225 pounds.

Coefficient of restitution (C.O.R.) was measured by firing the resulting golf ball is an air cannon at a velocity of 125 feet per second against a steel plate which is positioned 12 feet from the muzzle of the cannon. The rebound velocity was then measured. The rebound velocity was divided by the forward velocity to give the coefficient of restitution.

Shore hardness was measured in accordance with ASTM Test 2240.

Cut resistance was measured in accordance with the following procedure: A golf ball is fired at 135 feet per second against the leading edge of a pitching wedge, wherein the leading edge radius is {fraction (1/32)} inch, the loft angle is 51 degrees, the sole radius is 2.5 inches, and the bounce angle is 7 degrees.

The cut resistance of the balls tested herein was evaluated on a scale of 1-5. 5 represents a cut that extends completely through the cover to the core; a 4 represents a cut that does not extend completely through the cover but that does break the surface; a 3 does not break the surface of the cover but does leave a permanent dent; a 2 leaves only a slight crease which is permanent but not as severe as 3; and a 1 represents virtually no visible indentation or damage of any sort.

The spin rate of the golf ball was measured by striking the resulting golf balls with a pitching wedge or 9-iron wherein the club-head speed is about 80 feet per second and the ball is launched at an angle of 26 to 34 degrees with an initial velocity of about 110-115 feet per second. The spin rate was measured by observing the rotation of the ball in flight using stop action Strobe photography.

Initial velocity is the velocity of a golf ball when struck at a hammer speed of 143.8 feet per second in accordance with a test as prescribed by the U.S.G.A.

TABLE 10 Formulations INGREDIENTS 1 2 3 4 5 6 7 8 9 10 Surlyn 9910 438 — 486 486 486 — — — — — Surlyn 8940 1370 — 108 108 108 — — — — — Surlyn 8269 — — 832 — — — — — — — Surlyn 8265 — — 362 362 — — — — — — Surlyn White MB¹ 193 — 193 193 193 — — — — — Escor 4000 (Iotek 4000) — 904 — — — 300 400 500 — — Escor 900 (Iotek 8000) — 904 — — — 300 400 500 800 1000 Escor White MB² — 193 — — — 193 193 193 — — LDX-195 (Iotek 7520) — — — — — — — — 988 788 LDX-196 (Iotek 7520) — — — 832 1194 1188 988 788 — — PROPERTIES Shore C Hardness 93 95 85 82 79 78 81 85 84 87 Weight, grams 45.6 45.7 45.7 45.7 45.8 45.8 45.8 45.7 45.7 45.7 C.O.R. .821 .826 .808 .804 .803 .803 .805 .809 .807 .812 Riehle Compression 49 46 55 55 57 57 56 54 55 52 Barrel Cold Crack No breaks - any samples Cut Resistance 1-2 1-2 2-4 1-2 1-2 1-2 1-2 1-2 1-2 1-2 (1 = best, 5 = worst) SPIN PROPERTIES Spin Rate (rpm) 8707 8147 10037 10220 10451 10349 10057 9883 9903 9568 Laurich Angle 32.10 32.96 30.51 30.19 29.93 30.07 30.38 30.77 30.77 31.16 ¹Surlyn White MB (master batch) is comprised of 74.9% Surlyn ® 8528, 23.7% Unitane 0-110, .24% Ultra Blue, 1.05% Unitex O.B. and .03% Santonox R. ²Escor (Iotek) White MB (Master Batch) is comprised of 74.9% Iotek 4000, 23.7% Unitane 0-110, .24% Ultra Blue, 1.05% Unitex O.B., and .03% Santonox R.

Discussion of the Examples

The above examples indicate that the use of the acrylic acid based soft ionomers (i.e. the Iotek 7520 and the Iotek 7510 resins) in combination with relatively hard ionomers (i.e. Surlyn® 9910 and 8940, more preferably, Iotek 4000 or 8000) produce golf balls exhibiting higher C.O.R. values (i.e. thus better distance) while maintaining, and in many instances improving, the softness and playability characteristics of the balls when compared to golf balls produced with the methyacrylic acid based soft ionomers (i.e. Surlyn® 8265 and 8269) currently used in the Tour Edition® ball. In addition, the examples indicate that the improvements in softness and/or distance properties are produced without the expense of the cover composition's overall durability. As a result, the new ionomer cover formulations of the present invention produce golf balls which are longer in distance and softer than any other prior Spalding golf ball.

More particularly, Examples 1-2 represent golf ball cover compositions produced utilizing only hard ionomers. While these cover compositions produce golf balls exhibiting high C.O.R. (i.e. greater than 0.820) values, these balls are too hard to offer sufficient playability (Shore C Hardness greater than 90, and Riehle Compression less than 50).

Examples 3, 11-15 and 24 represent the hard-soft ionomer cover blends which are the subject of U.S. Pat. No. 4,884,814, and are essentially equivalent to the current Tour Edition® ball. Examples 12-15 vary depending on the type of methacrylic acid based soft Surlyn® ionomer utilized.

Examples 6-10 and 16-23 represent the hard-soft ionomer blends comprising acrylic acid soft ionomers. When compared to the prior art golf balls (i.e. Examples 3 and Examples 11-15), these golf balls have higher C.O.R. values, while exhibiting improved playability characteristics. This is particularly demonstrated in Examples 19 and 22, which are representative of the chemical composition of the Tour Edition® ball.

In addition, the data set forth in the Examples also indicate that the hard acrylic acid based ionomeric resins (i.e. Iotek 4000 and 8000), which are sodium or zinc salts of poly(ethylene acrylic acid), produce, when utilized with the acrylic acid based soft ionomers of the present invention, produce cover compositions exhibiting enhanced C.O.R. values (thus, improved travel distance) at the same or similar hardness when compared with hard methyacrylic acid based ionomeric resins (i.e. Surlyn® 9910 and 8940) which are sodium or zinc salts of poly(ethylene methacrylic acid). This can be seen in comparing Examples 6-10 with Examples 4 and 5. Thus, the more preferred compositions of the present invention comprise hard-soft ionomer blends comprised of acrylic acid based hard ionomeric resins with the acrylic acid based soft ionomeric resins. Furthermore, the data set forth in Table 7 indicates that slight improvements in C.O.R. values is produced when Iotek 7510 is substituted for Iotek 7520 (i.e. see Examples 28 and 29 in comparison to Examples 25 and 26). Moreover, the data demonstrates that use of Iotek 7510 alone and/or in combination with Iotek 7520 produces, when used in conjunction with hard ionomers, golf ball covers exhibiting higher C.O.R. values at similar hardness than those produced by known hard-soft ionomer blends.

Furthermore, the data set forth in Table 12 indicates that slight improvements in C.O.R. values is produced when Iotek 7510 is substituted for Iotek 7520 (i.e. see Examples 28 and 29 in comparison to Examples 25 and 26). Moreover, the data demonstrates that the use of Iotek 7510 alone and/or in combination with Iotek 7520 produces, when used in conjunction with hard ionomers, golf ball covers exhibiting higher C.O.R. values at similar hardness than those produced by known hard-soft ionomer blends.

In addition, because the acrylic acid based soft ionomeric resins available from Exxon under the Iotek designation (i.e. Iotek 7520 and Iotek 7510) contain no wax or other processing additives (i.e. it is believed that Surlyn® 8265 and 8269 use 0.5-1 wt. % of a bis-stearamide wax to prevent clumping and mixing during processing), fairly substantial cost savings can be produced due to the potential elimination of epoxy primer, thereby reducing volatile emissions and improving whiteness.

In addition to the above indicated test results, the distance and playability properties of the formulations utilizing acrylic acid soft ionomers (i.e. Examples 19 and 22, which are representative of the chemical composition of Spalding's longer distance and slightly softer, Tour Edition® 90 golf ball) were compared with various combinations of Spalding's Tour Edition®” (TE), Tour Edition® 100 (TE 100), and Top Flight® II (TF II) golf balls, as well as a number of competitive golf balls, and the following performance results were produced.

TABLE 13 DISTANCE TEST Club: 90 Deg. Metal Wood Driver   Club Head Speed (fps) 160 Launch Conditions Before Test After Test Launch Angle 8.3 N/A Ball Speed (fps) 239 N/A Spin Rate (rpm) 3232 N/A Turf Conditions Firm Firm and Dry Wind 1 mph 3 mph Temperature N/A 90 Relative Humidity N/A N/A TEST RESULTS BALL TYPE TRAJ. FT. CARRY DIFF. DEV. ROLL. TOTAL DIFF. TFII 13.1 6.4 254.8 0.0 0.6 18.5 273.3 0.0 TE 100 14.4 6.8 251.6 −3.2 2.0 15.5 267.2 −6.2 TE 90 12.8 6.5 251.6 −3.2 1.0 19.6 271.2 −2.1 TITLEIST BALATA 12.7 6.6 245.2 −9.6 4.5 21.0 266.4 −6.9 TITLEIST DT 12.9 6.6 250.0 −4.8 2.4 18.5 268.5 −4.8 MAXFLI ST 17.1 6.8 247.0 −7.8 −0.3 12.9 260.0 −13.4 MAXFLI BALATA 13.1 6.6 246.3 −8.5 1.7 19.9 266.2 −7.2 PRECEPT BALATA 15.4 6.8 247.3 −7.5 2.0 16.4 263.7 −9.6

TABLE 14 DISTANCE TEST Club: 5 iron   Club Head Speed (fps) 125 Launch Conditions Before Test After Test Launch Angle (deg.) N/A N/A Ball Speed (fps) N/A N/A Spin Rate (rpm) N/A N/A Turf Cond. Firm Firm Wind 4 mph 7 mph Temperature N/A N/A Relative Humidity N/A N/A TEST RESULTS BALL TYPE TRAJ. FT. CARRY DIFF. DEV. ROLL. TOTAL DIFF. TFII 24.1 6.0 177.8 0.0 2.1 17.3 195.1 −0.1 TE 100 23.1 5.9 173.9 −3.9 1.8 18.8 192.8 −2.4 TE 90 22.5 5.9 176.4 −1.4 2.8 18.8 195.3 0.0 TITLEIST BALATA 22.6 5.8 173.7 −4.1 4.4 21.0 194.6 −0.6 TITLEIST DT 22.5 5.9 176.6 −1.2 2.3 16.9 193.5 −1.7 MAXFLI ST 23.8 5.9 172.0 −5.8 2.5 19.4 191.4 −3.8 MAXFLI BALATA 23.9 5.8 173.5 −4.3 4.3 21.5 195.0 −0.2 PRECEPT BALATA 23.8 5.8 170.3 −7.5 3.6 20.8 191.1 −4.1

Comments: Statistical analysis of the results shows that for TE 90 vs. (4) of the competitive brands (Titleist Balata, Maxfli St., Maxfli Balata, Balata Precept) the differences in total distance are very significant. This means the longer total distance is likely due to differences in ball performance and is not due to random choice.

TABLE 15 SPIN TEST Full Standard Ball Type Square Hit¹ Deviation Tour Edition 9701 550 Tour Edition 100 10181 290 Tour Edition 90 9581 630 Top Flite XL 7635 772 Titleist 384 9775 99 Tour 100 Titleist Tour 100 9830 232 Titleist DT 90 7700 882 Maxfli ST 8228 735 Maxfli DDH 9276 231 Bridgestone 9050 253 Precept Wilson Staff 6989 719 ¹The full (square hit) was performed utilizing a Johnny Miller Finesse wedge with its face oriented for a square hit.

In view of the above test results, as well as additional data produced by internal testing, the following performance profile of the formulation comprising acrylic acid soft ionomers (i.e. Examples 19 and 22 concerning the softer Tour Edition® 90 golf ball) has been developed:

1. In machine tests, the Tour Edition 90 distance off the #5 iron and driver is longer than the current Tour Edition® 100 with slightly lower trajectory.

2. The Tour Edition® 90 is equal to the Top Flite® II in distance off the #5 iron and although two yards shorter than the Top Flite® II off the driver, it is significantly longer off the driver than the top competitive brands.

3. Spin off a full #9 iron is equal to the Tour Edition® and slightly less than the Tour Edition® 100.

4. Durability in lab testing is equal to the Tour Edition® or Tour Edition® 100.

The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. 

Having thus described the preferred embodiments, the invention is now claimed to be:
 1. A golf ball comprising a core and a cover, wherein said cover comprises: from less than 25 to about 10 percent by weight of at least one hard ionomer which is a sodium, zinc or lithium salt of the copolymer of an olefin having from 2 to 8 carbon atoms and an unsaturated monocarboxylic acid having from 3 to 8 carbon atoms, wherein said hard ionomer has a hardness greater than 50 on the Shore D scale and a flexural modulus of from about 15,000 to about 70,000 psi; and, from greater than 75 to about 90 percent by weight of at least one soft ionomer which is a sodium or zinc salt of a terpolymer of an olefin having 2 to 8 carbon atoms, acrylic acid, and an unsaturated monomer of the acrylate ester class having from 1 to 21 carbon atoms, wherein said soft ionomer has a hardness from about 20 to about 40 on the Shore D scale and a flexural modulus of from about 2,000 to 10,000 psi.
 2. The golf ball of claim 1, wherein the hard ionomer is a sodium or zinc salt of a copolymer of ethylene and methacrylic acid.
 3. The golf ball of claim 1, wherein the soft ionomer is a sodium or zinc salt of a terpolymer of ethylene, acrylic acid and methyl acrylate.
 4. The golf ball of claim 1, wherein said cover composition comprises from less than 25 to about 10 percent by weight of the hard ionomers and from greater than 75 to about 85 by weight percent of the soft ionomers.
 5. The golf ball of claim 1, wherein said cover composition comprises from less than 25 to about 15 percent by weight of the hard ionomers and from greater than 75 to about 85 by weight percent of the soft ionomers.
 6. The golf ball of claim 1, wherein said cover composition comprises from about 20 percent by weight of the hard ionomer and from about 80 percent by weight of the soft ionomer.
 7. The golf ball of claim 1, wherein said cover composition comprises from about 15 percent by weight of the hard ionomer and from about 85 percent by weight of the soft ionomer.
 8. A golf ball comprising a core and a cover, wherein said cover comprises a blend of from less than 25 to about 15 percent by weight of at least one methacrylic acid based hard ionomer and from greater than 75 to about 85 percent by weight of at least one acrylic acid based soft ionomer.
 9. A golf ball comprising a core and a cover, wherein said cover comprises a blend of from less than 25 to about 15 percent by weight of at least one hard ionomer which is a sodium or zinc salt of an ethylene, methacrylic acid, methyl or butyl acrylate terpolymer, and from greater than 75 to about 85 percent by weight of at least one soft ionomer which is a zinc salt of a terpolymer of ethylene, acrylic acid and methyl or butyl acrylate.
 10. The golf ball of claim 1, wherein said cover comprises a mixture of one or more pigments, an optical brighteners and/or dye.
 11. The golf ball of claim 8, wherein said cover comprises a mixture of one or more pigments, an optical brighteners and/or dye.
 12. The golf ball of claim 9, wherein said cover comprises a mixture of one or more pigments, an optical brighteners and/or dye. 